DMD's have found numerous applications in the areas of optical information processing, projection displays, and electrostatic printing. See references cited in L. Hornbeck, 128 X 128 Deformable Mirror Device, 30 IEEE Tran Elec. Dev. 539 (1983).
A great number of the applications described in Hornbeck, supra, use DMD's operated in a bistable mode as described in U.S. Pat. No. 5,096,279, incorporated by reference herein. The details of '279 will be summarized in some detail herein, but briefly in the bistable mode of a DMD a deflectable beam or mirror may be deflected to one of two landing angles, .+-..theta..sub.L, by underlying electrodes to which an address voltage is applied. At either landing angle (.+-..theta..sub.L) an extremity of the deflectable mirror lies in contact with an underlying device substrate. Generally, in one orientation, the deflectable mirror is "on", bright, or in other words reflecting light in the field of view. In the other orientation, the mirror is "off", dark, or not reflecting light in the field of view.
It has been discovered in prior art DMDs that a possible manufacturing defect is that of stuck mirrors. In such an instance, individual mirrors may not change between "on" and "off" states in response to changes in address and bias voltages. As such, the mirrors are always "off" or always "on". Always "on" defects or bright defects are particularly noticeable and objectionable. The defective pixels stick for a number of reasons including but not limited to: a defective addressing element underlying the mirror, a poor electrical connection between the mirror and a reference voltage, or a surface defect at the point of mirror contact.